Canonical Correspondence Analysis Axis Research Articles

Plant community formation and species distribution pattern in relation to environmental variables in Endiras Natural Forest, northwest Ethiopia

The study was conducted in Endiras Forest, northwest Ethiopia, to evaluate the effects of environmental variables on the patterns of plant community formation. A systematic random sampling technique was used to collect vegetation data from 56 (20 m × 20 m) plots laid at 100 m intervals on ten transects. In each plot, the species encountered and its percent cover abundance were recorded, which was later transformed into a modified Braun-Blanquet scale. The composite soil samples collected from 15 cm × 15 cm subplots were examined for 13 soil parameters. Communities were determined using cluster analysis. The Shannon-Wiener index was employed to quantify species diversity. The relationships between species and environmental variables were evaluated using canonical correspondence analysis (CCA). Seventy-three woody plant species, distributed in 40 families, were documented. Fabaceae was found to be the most species-rich family (20.55%). Five communities were generated from the cluster analyses that vary in diversity. Nine environmental variables were found to be significant in determining patterns of community formation (P < 0.05). Organic matter, pH, and altitude, highly correlated with CCA axis 1, largely shaped the community formation patterns. Various patterns of community formation demonstrate the need to design different conservation measures.

The drying of Lake Urmia and its consequences for waterbird assemblages

Summary The hypersaline Lake Urmia, located in Iran, has undergone a significant reduction in size and is currently facing the risk of desiccation. The decrease in water levels, coupled with elevated salinity levels, has initiated ecological degradation, leading to a substantial decline in the region’s waterbird population. This study employs breakpoint analysis to determine the year when the drought event affecting the lake commenced. Additionally, canonical correspondence analysis (CCA) is utilised to elucidate the interaction between environmental parameters and the waterbird assemblages in Lake Urmia over the period 1970–2018. Our investigation identifies the year 2000 as the initiation of the water crisis in Lake Urmia, synchronously coinciding with the decline in the waterbird populations. This finding highlights a significant connection between the majority of waterbird species and the axes of CCA, intricately linked with water availability within Lake Urmia. This revelation underscores the pivotal role of fluctuations in water levels in shaping the dynamics of the lake’s waterbird assemblages. Furthermore, our observations emphasise the importance of even minor improvements in hydrological conditions of the lake, resulting in substantial positive impacts on waterbird populations.

Macroinvertebrate assemblages along a gradient of physicochemical characteristics in four riverine wetlands, Upper Blue Nile basin, Northwestern Ethiopia

This study aims to examine the physicochemical variables that influence macroinvertebrate assemblages in wetlands of the Fetam River watershed. Macroinvertebrates and water quality samples were collected from 20 sampling stations across four wetlands between February and May 2022. Principal component analysis (PCA) was used to elucidate the physicochemical gradients among datasets and canonical correspondence analysis (CCA) was applied to explore the relationship between taxon assemblages and physicochemical variables. Aquatic insects such as Dytiscidae (Coleoptera), Chironomidae (Diptera), and Coenagrionidae (Odonata) were the most abundant families, and they comprised 20-80% of the macroinvertebrate communities. As demonstrated by cluster analysis, three site groups including slightly disturbed (SD), moderately disturbed (MD), and heavily disturbed (HD) sites were identified. PCA showed a clear separation of slightly disturbed sites from moderately and highly impacted sites. Differences in physicochemical variables, taxon richness and abundance, and Margalef diversity indices were observed along the SD to HD gradient. Phosphate concentration was an important predictor that influenced richness and diversity. The extracted two CCA axes of physicochemical variables accounted for 44% of the variability in macroinvertebrate assemblages. Nutrient concentration (nitrate, phosphate, and total phosphorus), conductivity, and turbidity were the main drivers of this variation. This suggested the need for sustainable wetland management intervention at the watershed level, ultimately benefiting invertebrate biodiversity.

Eco-assessment of streams of Konya closed river basin (Turkey) using various ecoregional diatom indices.

Ecological assessment of freshwater ecosystems based on diatom metrics is an important issue for attaining environmental sustainability. The present study aimed to evaluate differences in the diatom-stressor relationship in relatively least disturbed streams in the Konya closed river basin using multivariate analyses and to bio-assess streams by the application of different ecoregional diatom indices. Cocconeis euglypta, Cymbella excisa, Cocconeis placentula, and Achnanthidium minutissimum are the most contributing species to the dissimilarity of sampling stations between rainy (spring) and dry (summer and fall) seasons and also between altitude (A2 800- < 1600m and A3 ≥ 1600m) groups. The first two axes of canonical correspondence analysis revealed a significant (82.8%) relationship between diatom species and stressors. Diatom species displayed distinct responses to environmental variables (electrical conductivity, Ni, Cu, B, and altitude) playing important roles on the distribution of species. Diatom indices indicate different ecological statuses of stations, from bad to high. European diatom indices except Duero Diatom Index (DDI) and Trophic Diatom Index (TDI) showed good responses to the eco-assessment of streams and indicated high ecological status for the least disturbed sampling stations symbolized as S16, S20, S24, S25, S27-29, S37, and S39. These results were also supported by abiotic evaluation. Although TIT was more competitive in the bio-assessment of streams among diatom indices, it is necessary to increase its species list by determining their trophic weights in future studies. Therefore, the use of ecoregion-specific diatom indices is suggested along with increasing the number of used species to correctly interpret the water quality.

Eco‐assessment of Değirmendere and Bulaklı streams using diatom indices from different ecoregions

AbstractDiatom metrics are important tools for evaluating the environmental conditions of streams for the achievement of environmental sustainability. Aim of the present study was to assess the ecological status of Değirmendere and Bulaklı streams using diatom indices developed in different ecoregions and to elucidate responses of diatom assemblages to stressors using multivariate approaches. Analysis of similarity percentage indicated a 74% dissimilarity between Değirmendere and Bulaklı streams with the most contribution of Encyonopsis minuta, Achnanthidium minutissimum, Achnanthidium druartii, Amphora indistincta, and Gomphonema cuneolus species to this dissimilarity. The first two axes of canonical correspondence analysis exhibited a strong correlation (93.1%) between diatom assemblages and environment variables. Pollution‐tolerant species were associated with Bulaklı stream, whereas pollution‐sensitive species displayed relatedness to Değirmendere stream. Conductivity, salinity, oxidation–reduction potential, total phosphorus (TP), and orthophosphate were the significant effective environmental factors on the spatiotemporal distribution of diatom assemblages. Used diatom indices showed significantly positive and negative correlations with TP gradient. The results of bioassessment exhibited that diatom indices have different scores for the ecological status of the sampling stations. European diatom indices except Trophic Diatom Index and Duero Diatom Index mainly showed similar behavior in the bioassessment of ecological conditions of Değirmendere and Bulaklı streams. Among European diatom indices, Trophic Index Turkey was more competitive and could give better results in the bioassessment of streams. Results indicated that ecoregional specific diatom index could be used as a suitable tool to accurately evaluate the surface water quality.

Ecological assessment of Burç Reservoir’s surface water (Turkey) using phytoplankton metrics and multivariate approach

The present study aimed to elucidate relationships between phytoplankton species and stressors using multivariate approaches and assess the environmental condition of Burç Reservoir?s surface water using phytoplankton metrics from September 2018 to August 2019 according to implementations of the Water Framework Directive. Burç Reservoir had a characteristic of a warm monomictic pattern. Phytoplankton functional groups (E, F, J, LO, LM, MP , P, S1 , T, and W1 ) were found in the reservoir. A significant difference was found in total biovolume values changed from 2.28 mm3 /L in November 2018 to 0.51 mm3 /L in February 2019. The first two axes of canonical correspondence analysis explained 99.2% of relationships between stressors and phytoplankton assemblages. Explanatory factors such as electrical conductivity (EC), nitrate (NO3 -N), total nitrogen (TN), water temperature, calcium (Ca+2), precipitation, total organic carbon (TOC), ortho-phosphate (o-PO4 ), and total phosphorus (TP) significantly drove the spatiotemporal distribution of phytoplankton. Weighted average regression resulted that phytoplankton species such as Gymnodinium saginatum, Snowella lacustris, Ceratium hirundinella, and Pseudanabaena limnetica were closely associated with high TP, while Fragilaria capucina, Navicula trivialis, Cymbella aspera, Ulnaria biceps, Nitzschia palea, and Pseudopediastrum boryanum closely related to the EC. Carlson's trophic state index indicated that Burç Reservoir mainly has a eutrophic characteristic with the assessment of chlorophyll a, total phosphorus, and Secchi disk depth, while it had a eu-hypertrophic according to the OECD classification. Results of the modified PTI-phytoplankton trophic index (mean = 2.37), the Med-PTI Mediterranean phytoplankton trophic index (mean = 1.96), and the Q assemblage index (mean = 2.58) indicated a moderate ecological status of Burç Reservoir. The present study confirmed that phytoplankton assemblages are closely integrated with the environmental condition of Burç Reservoir, which could be assessed by using the PTI and Med-PTI.

Eco-assessment of least disturbed areas of the Antalya River basin: application of diatom indices from different ecoregions.

Biomonitoring of least disturbed areas is a crucial issue to accurately assess the ecological status of surface waters and ensure their sustainability. Diatom metrics are important tools for the assessment of environmental conditions of lotic ecosystems to achieve environmental sustainability. The present study was aimed to evaluate the ecological status of least disturbed areas in the Antalya River basin (Turkey) using diatom indices developed from different ecoregion. Diatom species such as Cymbella excisa, Achnanthidium minutissimum, Cocconeis euglypta, and Cocconeis placentula were the most contributing species to the dissimilarity of sampling stations between rainy and dry seasons. The first two axes of canonical correspondence analysis (CCA) elucidated a strong (86%) correlation between diatom taxa and stressors. Results of the Monte Carlo permutation test indicated that total phosphorus (TP), water temperature, Tin (Sn), total organic carbon, zinc, and pH are significantly influential ecological factors on the distribution of diatom taxa among sampling stations. The Spearman correlation rank test indicated that diatom indices had significant positive and negative correlations with TP gradient. Results revealed that diatom indices developed from different ecoregions have different scores for the eco-assessment of similar sampling stations. European diatom indices mostly showed similar behavior in the bioassessment of the ecological status of rivers in the Antalya region compared to the different ecoregion. Among European diatom indices, TIT was more competitive and could give better results in the bio-evaluation of rivers in the Antalya River basin. Using diatom indices developed from different ecoregions may lead to an erroneous assessment of water quality. Accordingly, ecoregional specific diatom metrics are needed to accurately determine the surface water quality. Eco-assessment of least disturbed areas of the Antalya River basin: application of diatom indices from different ecoregions: Abuzer Çelekli, Ömer Lekesiz, Tolga Çetin.

First assessment of lakes’ water quality in Aras River catchment (Turkey); Application of phytoplankton metrics and multivariate approach

This study is the first attempt to determine responses of phytoplankton assemblages to stressors using multivariate approaches and to evaluate the limno-ecological status of Aktaş, Çıldır, Aygır, Deniz and Balık lakes in the Aras River system (Turkey) using phytoplankton metrics according to the requirements of Water Framework Directive. Samples were collected in August and October of 2014, and June of 2015 by using the standard protocols. The first two axes of canonical correspondence analysis (CCA) elucidated strong correlations (λ1 = 0.937, 99.7% and λ2 = 0.763, 98.5%) between phytoplankton species and stressors with a 27.2% of the cumulative variance of species data. The Monte Carlo permutation test with the forward selection exhibited the significant effects of dissolved oxygen, orthophosphate (P-PO4), total phosphorus (TP), biological oxygen demand (BOD5), water temperature, nitrite (N-NO2), and altitude on the phytoplankton distribution among lakes. Lake Aktaş was closely related to N-NO2, TP, P-PO4, and BOD5 and characterized by species Messastrum gracile, Oocystis borgei, Treubaria triappendiculata, Snowella lacustris, Tetraëdron minimum, and Lemmermannia komarekii. They preferred N-NO2 higher than 90th percentile (0.026 mg/L) and TP higher than the 75th percentile (0.270 mg/L). Phytoplankton trophic index (PTI) scores varied from 2.06 in Lake Aygır to 2.36 in Lake Aktaş, while a range between 0.89 in Lake Aktaş and 1.81 in Lake Aygır was calculated according to Mediterranean phytoplankton index (Med-PTI). The correlations of PTI and Med-PTI (R2 = 0.94 and 0.90, respectively) with logTP gradient indicated congruent results. A high ecological status was found in Lake Çıldır, when Aygır, Deniz, and Balık lakes had good environmental conditions. Lake Aktaş showed a moderate ecological condition. The present study confirmed that phytoplankton assemblages closely integrated with the limno-ecological status of lakes in the Aras catchment, which could be assessed by using the PTI and Med-PTI.

Effect of habitat type on algal species diversity and distribution at high altitudes

To investigate how habitat type influences species diversity and distribution of algae, 115 sampling sites across eight different habitats (stream, spring, lake, pool, wetland, ditch, trough, hot-spring) were randomly sampled from Ağrı province, Turkey. A total of 392 algal taxa (gamma diversity) were identified, of which 212 taxa (54.08%) belonged to Bacillariophyta while the rest (180 taxa) belonged to seven other groups (Chlorophyta, Charophyta, Euglenophyta, Cyanobacteria, Miozoa, Ochrophyta, and Cryptophyta). 150 taxa were encountered only once. The highest alpha diversity was found in ditches (H' =4.57, 235 taxa) followed by streams (H' = 4.40, 238 taxa), and the lowest diversity was recovered in troughs (H' = 2.62, 42 taxa). Relatively high Whittaker's beta diversity (Bw = 19) indicated a low level of similarity among sampling sites suggesting that no common taxonomic group was solely effective enough to change dominancy level of any species among the habitats. The first two axes of Canonical Correspondence Analysis accounted for 58.1 % of the total variance in the occurrence of 152 algal taxa (all taxa recovered from more than three samples) and described gradients across four environmental variables (habitat type, pH, elevation and water temperature). Ditches significantly contribution to alpha and gamma diversity in the province although they have relatively small surface area and shallow water compared to other habitat types. High alpha diversity in ditches may be related to the positive effect of geographic and climatic factors in mountainous area. Future possibilities are discussed.

Bacterial and archaeal communities in deep sea waters near the Ninetyeast Ridge in Indian Ocean

Depth-dependent distribution patterns of bacterial and archaeal communities in deep sea water column around the Ninetyeast Ridge in the Indian Ocean were investigated using 16S rRNA gene profiling. Sampling was conducted at the northern Ninetyeast Ridge (1°59.89′N–9°59.70′S, 87°58.90′E–88°00.03′E) from September to November 2016 where samples were collected from the bathyal (1 000 m) to bathypelagic depths (>4 000 m) in four different stations. A total of 1 565 405 clean data falling into 6 712 bacterial OTUs and 1 452 727 clean data falling into 806 archaeal OTUs based on 97% similarity level were analyzed. Most of the bacterial 16S rRNA gene sequences were affiliated with Gammaproteobacteria, followed by Alphaproteobacteria and Bacteroidia. The archaeal 16S rRNA gene sequences mostly affiliated to Nitrososphaeria (Thaumarchaeota) dominated with relative abundances ranging from 52.68% to 97.2%, followed by Thermoplasmata (Euryarchaeota). Vertical partitioning of bacterial and archaeal communities among different water layers was observed. Canonical correspondence analysis (CCA) and Spearman’s correlations revealed that depth (P=0.003), dissolved oxygen (P=0.019), and nitrite (P=0.033) were the main environmental factors affecting bacterial community structure at genus level in the Ninetyeast Ridge. On the other hand, the first two CCA axes accounted for 74.4% of the explained total variance, it seems that the archaeal communities at genus level were heavily influenced by the environmental variables including depth, dissolved oxygen (DO), nitrite, salinity, phosphate, ammonia, nitrate, and silicate, but none of them exhibited any significant correlation on the structuring (P>0.1).

Biodiversity and distributions of freshwater mollusks in relation to chemical and physical factors in the thermokarst lakes of the Gydan Peninsula, Russia

Knowledge of factors affecting the diversity of benthic invertebrates is very important for biodiversity conservation, for monitoring, restoring and maintaining aquatic ecosystems. The purpose of this study was to investigate how the diversity and distribution of freshwater mollusks related to environmental factors. Twelve species of freshwater mollusks were identified during a survey of 15 thermokarst lakes in the Gydan Peninsula, Russia. Canonical correspondence analysis (CCA) was used to study the relationships between environmental variables and species abundance. The first CCA axis correlated with the content of macro-ions, mainly Mg2+, Na+, Cl−, substrate types, and plant remnants. Along the second CCA axis stations were ordered by depth and the presence of mosses. We found that the type of substrate, depth, abundance of mosses and hydrochemical parameters play an important role in the distribution of the mollusks in thermokarst lakes. These results expand our understanding of mollusks ecology in thermokarst lakes, and identify environmental stressors important for the performance of abiotic control.

Relationships between stand spatial structure characteristics and influencing factors of bamboo and broad-leaved mixed forest

ABSTRACTMoso bamboo is an economically valuable plant in southern China and bamboo and broad-leaved mixed forest is a better management model. The relationships between stand spatial structure characteristics and factors influencing (e.g., salt, soil, and terrain factors) bamboo and broad-leaved forest in the Nature Reserve of Tianbaoyan (Yongan city, Fujian provice), China, were investigated using canonical correspondence analysis (CCA). The results showed that the horizontal distribution of bamboo and broad-leaved forest was mainly randomly distributed, that the states of tree growth were at the doctrine of mean as a whole, and the degree of mixing by species was low. The first CCA axis accounted for slope position, soil organic carbon, crown ratio, bamboo density, broad-leaf tree density, soil water content, and C/N, while the second CCA axis showed variation due to altitude level, average diameter of broad-leaf tree, soil total nitrogen, and soil total phosphorus. In general, both axes reflected the response of forest spatial structure to changes in the water thermal gradient and the relationship between forest complexity and changing soil physio-chemical properties. Furthermore, the variation in stand spatial structure of bamboo and broad-leaved mixed forest explained by stand, soil, and terrain factors reached 100%. When broken down, interacting stand and soil factors together accounted for up to 67.3%, stand factors alone for 20.3%, and soil factors alone for 1.7%, while interactions among all three explained 9.69% of the stand spatial structure; terrain factors alone and their interaction with other factors had negligible explanatory power (0.09–0.21%).

Assessing macroinvertebrate communities in relation to environmental variables: the case of Sambandou wetlands, Vhembe Biosphere Reserve

The Vhembe Biosphere Reserve, South Africa, contains many wetlands that serve as wildlife habitats and provide vital ecosystem services. Some of the wetlands are continuously being degraded or destroyed by anthropogenic activities causing them to disappear at an alarming rate. Benthic macroinvertebrates are known as good water quality bioindicators and are used to assess aquatic ecosystem health. The current study investigated habitat quality using macroinvertebrate community structure and other biotic variables (i.e. phytoplankton, macrophytes) in relation to environmental variables in the Sambandou wetlands using canonical correspondence analysis (CCA). A total of fifteen macroinvertebrate families were identified over two seasons. The CCA highlighted seven variables, i.e. pH, phosphate concentration, temperature, ammonium, macrophyte cover, conductivity and water depth, which were significant in structuring macroinvertebrate community. Picophytoplankton and microphytoplankton concentrations decreased from winter to summer, whereas nanophytoplankton concentration increased from winter to summer. Thus, the dominance of small-sized phytoplankton indicated nutrient limitation and decreased productivity, whereas winter sites 2 and 3 were dominated by large-celled phytoplankton, highlighting increased productivity. Winter sites were mostly negatively associated with CCA axis 1 and were characterised by high temperature, phosphate and ammonium concentrations, macrophyte cover, pH and conductivity. Summer sites were positively associated with axis 1, being characterised by high water depth and pH levels. The results obtained highlighted that agricultural activities such as cattle grazing and crop farming and sand mining/poaching had a negative effect on macroinvertebrate community structure.

Environmental controls on shallow subtidal molluscan death assemblages on San Salvador Island, The Bahamas

Ecological studies that span multiple marine depositional environments frequently find that benthic invertebrate assemblages are correlated primarily with an onshore-offshore gradient. Variability within the same depositional environment is inferred to not result from water depth differences, but other parameters such as substrate consistency and shear stress. Modern studies focusing on assemblage variations within the same depositional environment can identify which variables affecting assemblage compositions are independent of water depth. This study examines the environmental controls on the composition of molluscan death assemblages from the shallow subtidal environments of San Salvador Island. Molluscan assemblages were tabulated from twenty-nine bulk samples collected from four locations around San Salvador Island representing seagrass meadows, open sandflats, and patch reef systems common in the shallow subtidal. In addition, quantitative environmental data for each sample was characterized, including seagrass density, water depth, temperature, pH, dissolved oxygen, and grain-size, as well as qualitative observations of wave energy and bioturbation. Cluster analysis and canonical correspondence analysis (CCA) were performed to identify environmental gradients associated with molluscan assemblage composition. Cluster analysis and CCA Axis 1 identify seagrass coverage and substrate consistency as the primary environmental variables describing molluscan death assemblage compositions. CCA Axis 2 identifies wave energy, bioturbation, and dissolved oxygen as the secondary environmental variables, though the small range of dissolved oxygen values (17–21 mg/L) collected using single, instantaneous measurements make it unclear whether the oxygen gradient is ecologically significant for our time-averaged assemblages. Our analysis demonstrates the variability of assemblages within a single depositional environment, as well as the utility of fine-resolution studies for identifying secondary environmental variables that control the composition of marine invertebrate assemblages.

Ecoregion approach in the assessment of aquatic ecosystems in the west of Gaziantep (Turkey): Application of diatom metrics

Abstract The biological assessment of surface water quality is becoming more important to evaluate the deterioration of aquatic ecosystems and to accomplish environmental sustainability since the implementation of EU Water Framework Directive (WFD). This study as the first attempt was organized to evaluate the ecological status of 17 freshwater bodies in the West of Gaziantep catchment by using diatom metrics. A total of 70 diatom assemblages were identified during the present study. The first two axes of canonical correspondence analysis (CCA) explained 0.962 and 0.945 of diatom assemblages–environment correlations for streams and reservoirs, respectively. According to the CCA, nutrients (e.g., P-PO4 and N-NO3) and metal ions (e.g. Cr, Ni, Pb, and Cu) strongly affected the distribution of diatom assemblages among the water bodies. Among the studied surface waters, Karanlik stream had the highest scores of 3.30, 3.39, and 2.39 due to the TIT–Trophic Index Turkey, TI–Trophic Index, and EPI-D–Eutrophication and/or Pollution Index-Diatom, respectively. The results indicated that this stream had a bad ecological condition when the EPI-D showed a poor condition. The occurrence of pollution-tolerant taxa, associated with high nutrients and electrical conductivity (EC), confirmed the ecological conditions of this stream. On the other hand, Cinarli (TIT = 2.23) and Yamacoba (TIT = 1.96) streams were of good ecological condition and had relatively low EC and nutrients. The presence of pollution-sensitive species in Cinarli and Yamacoba streams (Meridion circulare, Cymbella affinis, Halamphora veneta, and Cymbella excisa) endorsed the ecological status of it. The loading of organic and inorganic nutrients from livestock farming, agricultural land-use, and settlements could impact the water quality of the sampling stations in this catchment. The present study emphasized the importance of the evaluation of ecological integrity based on the biological and chemical characteristics of ecosystems. Diatom indices were used herein reflected efficient results for the separation of the ecological conditions of the sampled stations. Ecological preferences and occurrences of diatom assemblages and the significant positive correlation criterion with P-PO4 confirmed the suitability of TIT for assessing the ecological status of the sampling stations. All of these results suggest that the ecological status of water bodies should be evaluated due to the indices developed in their ecoregions.

Bio-assessment of surface waters in the south-east of Gaziantep (Turkey) using diatom metrics

Diatom metrics can be used to identify the ecological status of water bodies due to their good responses to anthropogenic disturbances. Our study is aimed to use diatom metrics developed from different ecoregions for assessing the ecological status of 11 surface waters in the south-east of the Gaziantep catchment (Turkey). Ecological characterizations of the sampling stations were introduced by Trophic Index Turkey (TIT), Trophic Index (TI), and Eutrophication and/or Pollution Index-Diatom (EPI-D). According to TIT and TI, Karkamış Reservoir had a good ecological condition while it had high ecological status based on EPI-D. This good ecological condition was approved by the presence of pollution sensitive species (e.g.,Cymbella affinis,Encyonema minutum,E. silesiacum,Cymbopleura amphicephala, andNavicula radiosa) and relatively low nutrients. Kayacık (TIT ranging 3.15–3.23) and Hancağız (TIT = 3.35) reservoirs had poor and bad ecological conditions, respectively. High nutrient, conductivity, and pollution-tolerant species (e.g.,Nitzschia amphibia,N. palea,N. umbonata,N. linearis,N. phyllepta,Tryblionella calida, andPinnularia brebissonii) supported the ecological statuses of the Hancağız and Kayacık reservoirs. The first two axes of canonical correspondence analysis explained 0.943 of relationships between diatom species and explanatory variables. Explanatory variables,e.g., calcium, conductivity, orthophosphate, nitrate, nitrite, sodium, pH, and sulfur, had strong impacts on the distribution of diatom assemblages among the sampling stations. TIT and TI separated ecological statuses of sampling stations in the south-east of the Gaziantep catchment, which correlated well with the evidence of water chemistry and response of diatom assemblages.

Long-term variation of the macrobenthic community and its relationship with environmental factors in the Yangtze River estuary and its adjacent area

Using data from four periods from 1959 to 2015, we report the long-term variation of the macrobenthic community in the Yangtze River estuary and its adjacent area. In total, 624 species were collected, and Polychaeta was the dominant group. Significant differences between the four periods were found. The CCA (canonical correspondence analysis) and RDA (redundancy analysis) results revealed that temperature, salinity, and depth significantly influenced the macrobenthic communities (89.6% of the species-environment relationship variance was explained by the first two axes of CCA and 94.3% was explained by RDA). The results of K-dominance curves (the elevation increased over time), ABC (abundance/biomass comparison) curves (the W value changed from 0.311 to 0.167 during 1959 to 2014–2015) and the Shannon-Wiener index (log base=2; 2.29–5.03 in 1959, 2.86–4.55 in 2000–2001, 2.28–4.56 in 2011–2012, and 1.79–4.43 in 2014–2015) showed that the ecological status of the benthic study area was deteriorating.

Water or sediment? Partitioning the role of water column and sediment chemistry as drivers of macroinvertebrate communities in an austral South African stream

Water pollution is a critical management issue, with many rivers and streams draining urban areas being polluted by the disposal of untreated solid waste and wastewater discharge, storm water and agricultural runoff. This has implications for biodiversity, and many rivers in the developing world are now considered compromised. We investigated benthic macroinvertebrate community structure and composition in relation to physico-chemical conditions of the water column and sediments. The study was conducted in an Austral catchment subject to both urban and agricultural pollutants in two different seasons. We assessed whether sediment characteristics were more important drivers of macroinvertebrate community composition than water column characteristics. We expected clear differences in macroinvertebrate community composition and in the associated community metrics due to distinct flow conditions between the two seasons. A combination of multivariate analyses (canonical correspondence analysis (CCA)) and biological indicator analysis were used to examine these patterns. Chironomidae was the most abundant family (>60%) in the upper mainstem river and stream sites. Stream sites were positively associated with CCA axis 2, being characterised by high turbidity and lower pH, salinity, phosphate concentration, channel width and canopy cover. Canopy cover, channel width, substrate embeddedness, phosphate concentration, pH, salinity and turbidity all had a significant effect on macroinvertebrate community composition. Using CCA variation partitioning, water quality was, however, a better predictor of benthic macroinvertebrate composition than sediment chemical conditions. Furthermore, our results suggest that seasonality had little effect on structuring benthic macroinvertebrate communities in this south-eastern zone of South Africa, despite clear changes in sediment chemistry. This likely reflects the relative lack of major variability in water chemistry compared to sediment chemistry between seasons and the relatively muted variability in precipitation between seasons than the more classic Austral temperate climates.

Vegetation composition differentiation and species-environment relationships in the northern part of Isfahan Province, Iran

A considerable proportion of Iran’s territory is covered with arid and semi-arid rangelands and mismanagement and overexploitation of those rangelands have resulted in serious ecological degradation. Thus, the need is pressing to examine the present species composition and the relationships with environmental factors for providing the needed scientific references to species conservation and ecological rehabilitation efforts. The aims of this study were to examine the species composition and to delineate the most important factors influencing the distributions of plant species and groups in the northern rangelands of Isfahan Province (Iran) using two-way indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA), principal component analysis (PCA), and canonical correspondence analysis (CCA). Field investigations were conducted in the growing season of 2014 using stratified random method in 22 homogeneous sampling units. In total, 75 plant species belonging to 52 genera and 19 families were identified. The most important families were Asteraceae and Papilionaceae, the most important genera were Astragalus, Cousinia, and Acanthophyllum, and the most important species were Artemisia aucheri and Artemisia sieberi. Plant species were classified into 10 groups using TWINSPAN. DCA was used to estimate the magnitude of changes in species composition along the first two ordination axes to provide gradient length estimations for PCA and CCA ordinations. The first three PCA axes and the first three CCA axes demonstrated similar cumulative percentage of variance, indicating that the environmental factors (selected by PCA) used in CCA ordination were acceptable for explaining the species composition and the distributions. CCA ordination showed that the first axis was closely related to elevation, slope, surface bare soil cover, surface litter cover, gravel proportion, organic matter, total nitrogen, CaCO3 content, and grazing intensity and that the second axis was closely related to sand proportion, silt proportion, clay proportion, and saturation percentage. Among these factors, elevation was the most effective factor to separate the plant groups and grazing was the major cause of rangeland degradation.

Population dynamics of Eichhornia crassipes (C. Mart.) Solms in the Nile Delta, Egypt

The present study aims to evaluate the growth and seasonal allocation of the biomass of water hyacinth (Eichhornia crassipes) under natural conditions in the south Mediterranean region (the Nile Delta, Egypt). In this study, the population characteristics (density, morphology and primary production) over a one‐growing‐season cycle were described. In the Nile Delta, the biomass of the shoot and root systems of E.crassipes was sampled monthly along three water courses from April 2014 to November 2014 using five quadrats (each of 0.5 m × 0.5 m) at each water course. The shoot system started to grow in April (121 g/DM/m2), reached a maximum biomass of 887 g/DM/m2 in July, and then decreased until reaching a minimum of 299 g/DM/m2 in November. The biomass of the root system increased from 75 g/DM/m2 in April to a maximum of 235 g/DM/m2 in August and decreased to a minimum of 100 g/DM/m2 in November. Water hyacinth allocated ca. 2% of its total biomass to stolons, 22% to laminae, 24% to roots and 52% to petioles. Peak density as high as 144 individual/m2 occurred in May, but it reduced to 33–50 individual/m2 during July to November. The average rate of change of biomass was maximum (17.3 g/DM/m2/day) during April and May and minimum (−8.9 g/DM/m2/day) during October and November. Relative growth rates were found to be lowest during the cooler months, October and November (−0.017 g/DM/g /day), whereas highest yields were recorded during the spring months, April and May (up to 0.044 g/DM/g/day). The correlation coefficients between the water characteristics and the first two canonical correspondence analysis axes indicated that the separation of the population parameters of water hyacinth along the first axis was negatively influenced by Zn. On the other hand, the second axis was positively correlated with electric conductivity, total N, total P, Mg, Na, K and Mn and negatively with pH.